Fixed radio access systems are currently employed for receiving direct satellite television broadcasts from satellites and for local telecommunication networks. Known systems comprise an antenna--popularly known as a satellite dish--and decoding means. The antenna receives the signal and provides a further signal by wire to a decoding means. In the case of fixed radio access telecommunications, subscribers are connected to a telecommunications network by a radio link in place of the more traditional method of copper cable. The radio transceivers at the subscribers premises communicate with a base station, which provides cellular coverage over, typically, a 5 km radius in urban environments. Each base station is connected to the standard PSTN switch via a conventional transmission link/network.
The decoder for each fixed radio access subscriber system will decode the received signal and encode signals to be transmitted, whilst in the case of a satellite broadcast receiving arrangement, the decoder will provide demodulated signals for a television receiver. The distance between the antenna and the decoder can sometimes be many meters apart; this can lead to a degradation of the received signal and either they require a larger receiving antenna; a higher power decoder; or a higher quality connector between the antenna and decoder. In many instances the solutions can be overly expensive and/or result in large apparatus being employed.
At a subscribers premises, the subscriber will require for a wireless in the local loop application: a handset, decoding means and an antenna, and for a satellite application: a set-top unit/decoding means and an antenna. Frequently the decoding means is combined with the antenna or the telephone facsimile receiver in a wireless in the local loop telecommunications but many difficulties arise. One solution has been to provide an integrated terminal and antenna arrangement.
In the case of wireless in the local loops, planning regulations and frequency allocation means that many systems operate or are planned to operate in the 400-800 MHz region. The wavelength in these frequency bands are 60-30 cm and terminals will be required to be much smaller than these dimensions.
At 450 MHz, a typical operating frequency, a dipole antenna would need to be half a wavelength in length which is of the order of 30 cm with a quarter wavelength monopole being only half of that again. The dimensions of the box can be equivalent to that of the antenna. A second antenna element can also be used to give receive diversity. One constraint of an integrated antenna and telephone/decoder is that shielding of electronic circuitry is required and such shielding can adversely affect the performance of the antennas. The circuitry can be bulky but should be enclosed in a structure designed taking aesthetic considerations into account, which may affect the orientation of an antenna with respect to the shielding enclosure.
Presently some terminals sit flat on a desktop, but this can be a serious limitation, especially when antenna lengths can be up to 40 cm. Telrad of Israel presently produce such an example with their CET-10 model which possesses a fixed, vertically oriented half wavelength omnidirectional main antenna and a second diversity antenna which comprises an internally mounted printed circuit antenna. In addition to being designed to be operable on a desk or similar horizontal surface, the terminal should be operable whilst mounted on a wall or similar vertical surface, when the terminal body and monopole will both be vertical.
Another known wireless in the local loop arrangement is a desk top terminal manufactured by the Mitsubishi Corporation which possesses two omnidirectional antennas. These antennas are half wavelength monopoles which, together with matching networks are each some 25 cm in length. The antennas are vertically oriented in a spaced apart fashion on the terminal housing which encloses an associated earthed box which houses electrical control circuitry.
When the antennas are mounted as described, in the above two cases, the radiation pattern currents are not optimised whereby an uncontrolled azimuth pattern is obtained which is of mixed polarisation resulting in nulls in the azimuth plane.